For many years, plastic containers have done well in holding and conveying products to market. Containers used for food storage often have features to seal in product freshness. One such feature is a seal between the lid of the container and the container itself. This seal can add to the product freshness when the seal is used to reduce the air space between the food product and the top of the container.
Some containers have an added thin, heat-sealed film of plastic over the mouth of the container. These heat-sealed films have proven to be very good at sealing containers, but do not change the amount of bacteria already in the product inside the container at the time of sealing. Some container manufactures have added nitrogen gas under the film before heat-sealing to reduce food contamination. By adding nitrogen gas, growth of aerobic bacteria is reduced. However, the use of nitrogen gas is difficult to control and adds additional cost to the product. Eliminating any air space completely within the container would be a superior method if the container could withstand negative pressure without distorting the side wall or cracking the container. This pressure may cause the container to crack or break at weak points.
Another method of protecting a food product within a container is to introduce the film-sealed container to extremely high-pressure HPP (High Pressure Pasteurization) that kills the bacteria inside the product. The HPP method uses 90,000 pounds (˜40,000 kilograms) of rapidly pulsing water pressure to destroy bacteria within the container. This method works well to extend the shelf life of the product, but can also crack and destroy a plastic container if it does not have features to accommodate extremely high and/or low pressures within the plastic container. Furthermore, HPP methods are costly to run in production.
Another new development in food safety and container technology is to place the container and product under a vacuum just before the container is closed with a heat-seal. Vacuum sealing plastic containers also works well at extending the shelf life of food products, but the disadvantage is that plastics, such as PET or polypropylene, distort easily under pressure, especially when the container walls are thin, leaving an aesthetically displeasing container after vacuum sealing.
Therefore, there remains a need to create containers that can withstand high pressure and vacuums that prevent side wall distortion, and cracking of the container and base of the container.